What's the Name of That Book??? discussion

Fantasy book read around 1990 in Texas with the Paper hard cover of a hot air balloon holding a wooden ship or boat with a man looking your direction and many other similar air craft in the background high above a world or possibly between 2 worlds with a shared atmosphere. The story is about 2 adult brothers. They live on a planet with almost no metals and have to use hard wood trees and their wood in place of metals. Their planet shares a atmosphere with a smaller planet/moon that they believe their Souls travel to after death. One is the Older brother, a scientist and the other younger brother is in the military. As i remember it, most of the book is about the younger brother in the military. Or it could be that the younger brother had a more interesting story to me. In the story as I remember it there are monster/creature/animals that are called (Perth/Terth)?Bubble or balloon like creatures. Possible (view spoiler)[ That apparently have a symbiotic relationship with the hardwood trees that the people need to harvest for metal substitutes and crystals that have chemical properties. The (perth/Terth) release spores when they rupture killing or sickening anyone that are close to them when they self destruct and spread their spores (Warning - I could be completely wrong about the names of (perth/Terth). As I remember (I could be mixing this up with one of the thousands of books i have read) the crystals in the base of the trees that are in separate chambers that have Alchemical properties. Combining 2 different crystals makes a heat source and other chemical like effects.
The older scientist brother is trying to figure out a solution to the (perth/Terth) problem. The younger Larger brother that is suggested to have a different father than the older scientist brother is a tough military hotshot that is involved in protecting workers that harvest the trees from the (perth/Terth). (view spoiler)[ After the (perth/Terth) become even more evolved and dangerous they devise a plan to evacuate the planet to the moon/planetoid that shares their atmosphere with hot air balloons that can work in the zero gravity between the two planets. There are riots and revolts about the Aeronauts desecrating the place of the dead by going physically to the moon as their society collapses (view spoiler)[ In the last days before the evacuation the Older scientist brother is killed by the (perth/Terth) in a accident or experiment, but before he dies he asks his younger brother to take his wife with him on his ship so she will survive. during the trip to the moon the younger brother and his newly widowed sister in law have sex. When they arrive on the smaller planet they find metals laying on the surface of the ground obviously very plentiful and harmless versions of the (perth/Terth). The end. (hide spoiler)] (hide spoiler)] (hide spoiler)]

Sounds like Bob Shaw's The Ragged Astronauts - first in a trilogy

Oh my Gosh!! That's it ! You are a mental health hero! =) Solved!

Glad you found your book, Danny. Here's the link for Genesistrine's find - The Ragged Astronauts by Bob Shaw.

Danny wrote: "Oh my Gosh!! That's it ! You are a mental health hero! =) Solved!"

Glad to help!